Brake system for a vehicle driven by at least one hydraulic motor fed in a closed circuit

Abstract

A method of operating a brake system for a hydraulic motor, by feeding the hydraulic motor with at least one pump having a variable cubic capacity, in a closed circuit, providing a friction brake to brake the motor, providing a brake controller that controls an amount of applied frictional braking by the friction brake and an amount of applied hydraulic braking, and determining a level of actuation of the brake controller to detect normal and emergency braking situations. In normal braking situations, the proportional amount of frictional and hydraulic braking is managed as a function of parameters to cause progressive hydrostatic braking to occur by causing a ratio between the fluid flow rate delivered by the pump and the active cubic capacity of the motor to decrease progressively. In emergency braking situations there is a controlled sudden decrease in the ratio between the fluid flow rate delivered by the pump and the active cubic capacity of the motor, and then progressive hydrostatic braking occurs. The friction brake is activated during both normal and emergency braking situations.

1. A method of operating a brake system for a hydraulic motor, the method comprising:
 feeding the hydraulic motor with at least one pump having a variable cubic capacity, in a closed circuit; 
 providing a friction brake to brake the motor; 
 providing a brake controller that controls an amount of applied frictional braking by the friction brake and an amount of applied hydraulic braking; 
 determining a level of actuation of the brake controller to detect normal and emergency braking situations; 
 in normal braking situations, managing the proportional amount of frictional and hydraulic braking as a function of at least one input parameter, to cause progressive hydrostatic braking to occur by causing a ratio between a fluid flow rate delivered by the pump and an active cubic capacity of the motor to decrease progressively; 
 in emergency braking situations, causing a controlled sudden decrease to take place in the ratio between the fluid flow rate delivered by the pump and the active cubic capacity of the motor, and then causing progressive hydrostatic braking to occur; and 
 activating the friction brake during both of said normal and emergency braking situations. 
 
   
   
     2. The method according to  claim 1 , wherein, in emergency braking situations, the controlled sudden decrease in the ratio between the fluid flow rate delivered by the pump and the active capacity of the motor is caused by a sudden decrease in the fluid flow rate delivered by pump. 
   
   
     3. The method according to  claim 2 , wherein the sudden decrease in the fluid flow rate delivered by the pump is caused by a sudden decrease in the cubic capacity of the pump. 
   
   
     4. The method according to  claim 3 , further comprising:
 determining an amount of the sudden decrease in the cubic capacity of the pump as a predetermined proportion of the active cubic capacity of the pump at the time of braking. 
 
   
   
     5. The method according to  claim 2 , wherein the at least one input parameter is selected from the group consisting of: the level of actuation of the brake controller, a speed of a vehicle powered by the motor, an active cubic capacity of the pump, and the active cubic capacity of the motor. 
   
   
     6. The method according to  claim 1 , further comprising:
 providing the hydraulic motor with a plurality of active operating cubic capacities; 
 when braking is caused to take place while the motor is in a small active cubic capacity, managing the proportional amount of frictional and hydraulic braking to cause the motor to go over to a larger active cubic capacity when the value of the active cubic capacity of the pump is less than or equal to a limit value; and 
 increasing a value of said active cubic capacity of the pump to a value determined as a function of the motor going over to said larger active cubic capacity preventing said motor from generating a sudden decrease in the speed of the motor, and for progressively decreasing the cubic capacity of the pump from said determined value. 
 
   
   
     7. The method according to  claim 6 , further comprising:
 in normal braking situations, managing the proportional amount of frictional and hydraulic braking to maintain the cubic capacity of the pump at a given value corresponding to the motor being allowed to go over to its large active cubic capacity, for a stabilization lapse of time, before causing the motor to go over to the larger active cubic capacity; and 
 in an emergency braking situations, decreasing or substantially canceling the stabilization lapse of time. 
 
   
   
     8. The method according to  claim 7 , further comprising, in emergency braking situations, causing said motor to go over said larger active cubic capacity, after suddenly decreasing the fluid flow rate delivered by the pump. 
   
   
     9. The method according to  claim 6 , further comprising, in emergency braking situations, causing a sudden decrease to occur in the ratio between the fluid flow rate delivered by the pump and the active capacity of the motor to cause said motor to go over to said larger active cubic capacity, after the sudden decrease in the fluid flow rate delivered by the pump. 
   
   
     10. The method according to  claim 6 , further comprising:
 providing a vehicle having a plurality of displacement members, disposed in succession in the direction in which the vehicle travels, and each displacement member being driven by at least one hydraulic motor; 
 managing the proportional amount of frictional and hydraulic braking of the at least one hydraulic motor for a single displacement member to go over to a maximum active cubic capacity prior to or at the time of braking, without modifying the active cubic capacity of the at least one hydraulic motor that drives the other displacement members. 
 
   
   
     11. The method according to  claim 1 , wherein, in emergency braking situations, the controlled sudden decrease in the ratio between the fluid flow rate delivered by the pump and the active capacity of the motor is managed as a function of said at least one input parameter. 
   
   
     12. The method according to  claim 11 , wherein the at least one input parameter is selected from the group consisting of: the level of actuation of the brake controller, a speed of a vehicle powered by the motor, an active cubic capacity of the pump, and the active cubic capacity of the motor. 
   
   
     13. The method according to  claim 1 , wherein the at least one input parameter is selected from the group consisting of: the level of actuation of the brake controller, a speed of a vehicle powered by the motor, an active cubic capacity of the pump, and the active cubic capacity of the motor. 
   
   
     14. The method according to  claim 1  further comprising:
 providing an auxiliary engine to drive the pump; and 
 managing the proportional amount of frictional and hydraulic braking to cause a drive speed of said engine to be reduced at least at a beginning of a braking stage. 
 
   
   
     15. The method according to  claim 1 , further comprising:
 providing an actuatable control member; 
 providing at least two brake members constrained to rotate respectively with a rotor and with a stator of the motor; 
 providing an actuator with a moving portion which co-operates with one of said two brake members to urge the at least two brake members into friction contact with each other as a function of fluid pressure in the actuator; and 
 determining a level of actuation of the brake controller to detect the amplitude of actuation of said control member or the fluid pressure in the actuator. 
 
   
   
     16. The method according to  claim 1 , further comprising:
 monitoring fluid pressure in a feed duct of the hydraulic motor that is at high pressure during the braking stage; 
 and using the monitored fluid pressure as at least one of said at least one input member.